Geographic variation in body size has been studied in the context of Bergmann's and Allen's ecogeographic rules, which relate changes in body and appendage sizes to temperature fluctuations associated with latitude and altitude. Moreover, organisms adapted to high-altitude exhibit blunted hematological responses, promoting survival in hypoxic environments. We collected 117 adult Slate-colored Coots (Fulica ardesiaca), representing both color morphs (68 chestnut-fronted and 49 pale-fronted) and sexes (49 males and 68 females), and sampled at three latitudinal (north, central, and south) and two altitudinal (low and high altitude) levels in the Peruvian Andes. Given the absence of geographic variation in morphometric and hematological traits across color morphs and sexes, we grouped these data together. We then used linear mixed models to assess latitudinal and altitudinal variations in body size (body mass and skull length) and appendage size (relative wing chord, tarsal and culmen lengths adjusted for both body mass and skull length). The same models were applied to analyze altitudinal variation in hematological traits (hemoglobin concentration, hematocrit, and mean corpuscular hemoglobin concentration). Our findings corroborated Bergmann's and Allen's rules, showing variation in body and culmen size across elevational and latitudinal gradients. No significant differences (P < 0.05) were observed in the three hematological traits, suggesting that polycythemia is not a necessary response to hypoxia in this species. Depending on when these coots first inhabited high altitudes, our results might support the hypothesis of duration of high-altitude ancestry, suggesting that species residing at high altitudes for longer evolutionary periods might be better adapted.